The present invention is directed to an optical article with optical multi-aperture operation. More specifically, the present invention is directed to an optical article with optical multi-aperture operation having electrically conductive and selectively passivated patterns.
Optical articles, which may transmit various forms of radiation, are in demand in various industries. Examples of industries where optical articles are used include the electronics, nautical and aeronautics industries. Optical articles include windows, domes, and lenses, which are used to protect electronic devices on terrestrial, nautical and aeronautical vessels from undesired electromagnetic interference as well as other forms of radiation that may interfere with the optimum performance of such devices.
A process known as chemical vapor deposition (CVD) is often used to fabricate optical articles. The CVD process includes the steps of directing reactant gases into a reactor vessel disposed at elevated temperatures and chemically reacting the gases to form the material. The material is deposited over a substrate to provide the particular optical article. The CVD process is a continuous process in which new reactant gases are introduced into the vessel and by-product gases and un-deposited material vapors are vented. The combination of the reactants and by-product gases as well as the elevated temperature provides a highly corrosive environment.
Many optical articles have either layers or gratings buried within the articles. Such layers or gratings may be used for heating to de-ice the optical article, provide electromagnetic shielding, or provide electromagnetic absorption. Such layers also may be used to provide a surface reflective to one or more wavelength bands of incident electromagnetic energy. Optical articles such as bandpass filters and dichroic beam splitters, which require a pair of surfaces reflectively responsive to different electromagnetic wavelengths, may be fabricated having one or more buried reflective layers.
When the optical article is fabricated by providing a chemical vapor deposited material over a reflective or conductive surface, the high temperatures and the chemically corrosive environment often degrade the surface morphology of the highly reflective or conductive materials. Further, when layers of the highly reflective metals such as gold or silver are used, the high temperatures and corrosive environment of the CVD process causes the layers to agglomerate. When first deposited, these metals tend to have a mirror-like, smooth and hence a reflective surface. However, during CVD, small islands of the material are formed leaving behind holes previously occupied by the material. Additionally, for some materials such as silver, total removal of the layer often occurs. This degradation in the surface morphology leads to reduced conductivity and reflectivity of the buried layers. Typically, high conductivity and reflectivity are the most important properties of these buried layers. Accordingly, buried layers containing highly reflective and conductive materials are not readily found within optical articles fabricated from chemically vapor deposited materials.
U.S. Pat. No. 4,772,080 discloses optical elements with buried layers prepared using CVD methods. The elements are composed of a base layer, an intermediate layer over the base layer, which is composed of a refractory material and an overcoat of a CVD deposited material. The base and the overcoat layer of CVD material may be silicon, germanium, group III-IV materials, aluminum oxynitride, zinc sulfide, zinc selenide, yttrium oxide and magnesium oxide. The intermediate layer may be tungsten, molybdenum, tantalum, titanium, and rhodium, or dielectrics such as borides, carbides, nitrides, oxides or silicides.
The patent also discloses that the elements have a base, a passivating layer of refractory material over the base, a conducting layer over the passivating layer and a second passivating layer of refractory material over the conducting layer. A CVD deposited material forms a coat over the conducting layer. The pair of passivating layers may be composed of refractory type metals or refractory dielectrics. The conductive layer may be composed of a refractory type of metal such as tungsten, or a metal such as copper, silver, gold, platinum, palladium or aluminum. The patent states that the passivating layers protect and isolate the conductive layers from elevated temperatures and corrosive chemicals during CVD processes when coating the article with the overcoat layer.
A disadvantage of the optical elements disclosed in the patent is that the passivating layers completely encompass the intermediate region with the electrically conductive refractory metals. These passivating layers completely isolate the electrically conductive refractory metals from both the base layer and the overcoat layer. Because the materials that compose the passivating layers are different from the materials that compose both the base and overcoat layers, refractive indices of radiation transmitted to and from the optical elements change at the interface of the passivating layers and the base and overcoat layers. The change in the index of refraction of the radiation compromises the accuracy and over all performance of the optical elements. Radiation is reflected at the refractive index change boundary, thus reducing the overall transmission of the optic. In addition, radiation is bent as it passes through the passivation layer, due to the different refractive index, causing image distortion.
Another problem associated with the intermediate region of the optical elements is the bond interface between the passivating layers and both the base and overcoat layers. Since the materials, which compose the passivating layers and the base and overcoat layers are different, a weak bond is formed between the passivating layer and the overcoat and base layers. This weak bond may result in the separation of the passivating layers from both the overcoat and base layers compromising operation of the optical elements or completely disrupting their operation.
Accordingly, there is a need for improved optical articles and methods of making the same, which have an improved design and transmission.